Influence of excess titanium on hot ductility of C-Mn-Cr-Al steel

The effect of excess titanium (Ti/N ratio in the range 5-10) on the hot ductility of C-Mn-Al steels has been investigated. Precipitates in the Ti bearing steel mainly consisted of Ti4C2S2 and TiCyN1-y. The former was usually more than 50 nm and precipitated along the grain boundaries, and the latter was less than 50 nm and dispersed extensively in the matrix during strain. The effect of excess titanium on ductility depended on whether TiCyN1-y or Ti4C2S2 was the preferred precipitate. The fine precipitation of TiCyN1-y caused a deterioration in the ductility and a wider ductility trough. In contrast, preferential precipitation of Ti4C2S2 either had no marked influence or caused only a slight improvement in the ductility because precipitates of Ti4C2S2 are coarse and more stable than MnS, removing more sulfur from the matrix and boundaries. Based on a thermodynamic calculating model, the amount of equilibrium precipitation was calculated and the preferential precipitation in Ti added steels has been predicted.